You should think about it. When going uphill, you walk backwards, and when you come back, it becomes downhill. The original downhill road has become an uphill road.

So the distance up and down the mountain has changed, and the speed up and down the mountain has not changed, so the time will definitely change.

I remember choosing B, because there is no map, so I can't calculate it in detail.

Ignore the smooth road (because the speed and distance of this road are the same, it is convenient to explain). Set uphill road s 1 and speed v1; Downhill s2, speed v2.

Then the total time to go is t=s 1/v 1+s2/v2.

Total running time t'=s2/v 1+s 1/v2.

Of course not!

I hope it helps you. I typed so many words.